San Diego Natural History Museum--Your Nature Connection[San Diego County Bird Atlas Project]

WRENDERINGS
The quarterly newsletter for Bird Atlas volunteers
Summer 2000

In this Issue
What Bird Is That!?! The Story of San Diego County's First Confirmed Nesting of the Yellow-headed Blackbird

Notable Observations

Reports from the Field
Brown-headed Cowbird Banding Project
The Last Holdouts
The Helicopter Trip to Santa Rosa Mountains - Take 3

Focus On...
Royal and Elegant Terns

Progress Report

News and Updates
Blockbuster Weekends
WindDing Things
Birds of the World: A Checklist
Thanks to our Supporters



Yellow-headed Blackbird

What Bird Is That!?! The Story of San Diego County's First Confirmed Nesting of the Yellow-headed Blackbird

Jim Wilson and I were separated by about 150 yards along the north side of a two-acre patch of cattails. Jim was playing his Virginia Rail tape in the distance when I heard a noise that sounded like an angry "broody" hen. One gets this call when egg gathering requires ejecting a broody hen from a common egg-laying nest. Jim came back and listened. "Don't know about broody hens, but it sounds like someone being strangled and yelling for help." Of course, by now you all know what bird was hidden in the tules.

When we went to the south shore of the lake we confirmed what we suspected: Yellow-headed Blackbirds. The tules on the south shore are in small separated patches, generally 30 to 50 feet in length, parallel to the shore, and extending a maximum of 30 feet into the lake. We dwelled where one pair was occupying a corner of one of these smaller patches. The male perched in the upper portion of the tules, occasionally flying to the shore to feed. The female flew to shore both to feed and to gather nesting material. The female repeatedly returned to the same region within the lower parts of the tules, immediately below the male. Occasionally the male would drop down into the tules as if to check on the nest building's progress or perhaps offer advice.

The male's perching location and attitude were very similar to that of the Red-winged Blackbirds in the same tules and at the same time. There was a significant difference in nest-site preference between the Redwings and the Yellowheads. Redwings and Tricolored Blackbirds seem to prefer the central portions of nesting-site vegetation patches, whereas we observed the Yellowheads preferring the outside edges of patches. We also observed a regular "percher" on a thin island of tules, too thin to appeal to the other blackbird species.

We observed at least three definite pairs of the Yellow-headed and a total of 15 individuals. If we had spent less time on one pair and more time on an overview of the entire site we likely would have seen at least 30 to 45 Yellow-headed Blackbirds. In addition to multiple singing males we observed several territorial disputes, one simultaneously involving three males. One of the three was the male we were observing closely.

The adult male is a striking bird whose bright yellow head and breast and white wing patch contrast sharply with a jet-black body. He also occasionally exhibits another striking feature. When he bends over to feed, up goes the tail and a bright yellow circle around his anal opening flashes. What use is this? Could it have evolved as a false eye to ward off a predator's attack while the bird is in a vulnerable position? This yellow anal circlet was not mentioned in any of the bird books carried by those of us at the spring blockbuster in our evening discussion.

On this date the Redwings were on the nest or with young. I verified this two weeks later when I observed a Raven raid a Redwing nest and carry off a young while the male Redwing was in futile hot pursuit. The Tricolors, males and females, were leaving the tules to feed in adjacent fields and thus had not nested yet. Also at the known colony site in Jacumba (U28) I verified that the Tricolors were not yet nesting.

The three species of blackbirds observed seem to be synchronous nesters, i. e., all the flock members laying eggs at virtually the same time, in contrast with asynchronous breeders like doves and House Sparrows. The atlas project's database will provide insight into the degree of synchronism of breeding by similar species in similar environments.

The Yellow-headed Blackbird nesting site is at a lake at 3240 feet elevation in square T28, Bankhead Springs. The lake is large for the region with a 2-acre cattail patch and many smaller patches. The site lies on a large private ranch whose owners severely restrict access; thus the site experiences little disturbance. Our getting permission to visit this ranch is a rare privilege.

Simultaneously with our first audio contact with the Yellowheads we heard a Least Bittern. It was making (from the National Geographic field guide) "a softer series of ku notes heard only on the breeding ground." Certainly not a breeder I expected in the high desert. Stumbling on the unexpected, however, makes birding interesting and varied--birds don't read the books.

I spend the summer and fall in Montana. The Yellowheads will be on nests there in June, and I intend to observe and compare their nesting habits with those in the Boulevard area.

--Frank Unmack

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